Im so sorry if the question looks like bait I was just genuinely curious about what was your opinion on it.
Thank you for telling me this.
The reason I was suspicious is because Turtle On Turtle has become extremely touchy and controversial since the fandom got invaded by the anti-shipper cult, who actively went around making death threats against writers and artists because they tried to equate "mutant turtles" with "real humans" and were unable to reconcile the "teenage" part with the "they're turtles and they age in canon and they don't age like humans and have we mentioned they're turtles" part.
Okay. See. There's been a scary, dangerous mindset of: "we're anti and since we believe fiction directly influences reality, these fantasy creatures mutated via unknown alien mutagens are just like real people, and we can assign moral taboo values to them that make little to no logical sense, and we say that anyone who writes about them having sex with each other is evil, perverted, wishes to see incest in real life, and must die in various horrible ways, including having their kneecaps devoured, stepping on spiked Legos, getting an axe to the chest, being beheaded, being poisoned, etc, because the emotional attachment we personally have to these fantasy creatures extends to hoping our self insert OCs will be with them which can't happen if they're with each other"...
...to which the older members of the fandom respond, "okay but have you heard of polyamory, pansexuality, and imagination? it's all the rage. also, it's fiction, they're turtles, and they're mutants borne of alien goop. And not real."
Plus, canonically, they're on the asexual spectrum. (and at the end of the last unfinished volume of Mirage, pansexual Michelangelo had sex with an alien reptilian princess who laid eggs that may or may not be Mikey's.)
The "brotherhood" part was always about clanhood, because it wasn't said if the four turtles came from the same clutch. In the wild, turtles will fuck each other anyway, and in some TMNT fanfiction, the guys have mating seasons. There are no rules. It's a great mix of urban fantasy and "well, uh, biology probably doesn't work like that but that's why there's unstable alien mutagens involved. Time to get weird."
However, none of that matters to the cultists, who respond with alarmism, accusations, and fear. Even now with asexuality headcanons everywhere, there is this bizarre kind of gatekeeping over of all things mutant turtles fucking each other. That was a weird sentence to type.
So, mentioning tcest on Tumblr in the last few years is a toss up between "do I feel like dealing with shrieking angry people between the ages of 14 and 29 who are creepily invested in all the wrong ways in complaining about the fictional sex lives of alien mutant turtles" and "this is such a weird wild thing to write about, but holy shit what a beautiful psychoanalysis of endangered monsters and aliens and the story itself is epic and heartwrenching awwww it's adorable"
And despite what antis like to say, no "tcester" has ever pressured anyone to read their stuff, because they're respectful enough to know it's a weird niche, and you know what if I find out that someone did, I'll fire them out of a cannon into the sun, because the second rule of fanfiction is "tag your fics" IE "for the love of squick, warn for kinks and slash" - there are authors out there who don't, and it's really disturbing. Hatred of tcest is fine and good to know! Hardcore threats against fans of it is ugly, nonsensical, immature, sophomoric, and bratty. What I've discovered is that anti-tcesters are disingenuous and predatory and will go to lengths to harm artists while proclaiming moral superiority, and that's probably why I saw your question as bait.
This has been a fandom history lesson from my memory banks, upon which I will now lie and stare at the fogginess creeping in from thirty years ago.